TIDUF14 October   2022

 

  1.   Description
  2.   Resources
  3.   Features
  4.   Applications
  5.   5
  6. 1System Description
  7. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
    3. 2.3 Highlighted Products
      1. 2.3.1 BQ76952
      2. 2.3.2 LM5163
      3. 2.3.3 MSP430FR2155
      4. 2.3.4 ISO1042
      5. 2.3.5 TPS54308
      6. 2.3.6 ISO7731
      7. 2.3.7 THVD1400
      8. 2.3.8 UCC27524
      9. 2.3.9 TMP61
  8. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Hardware Requirements
    2. 3.2 Test Setup
    3. 3.3 Test Results
      1. 3.3.1 Cell Voltage Accuracy
      2. 3.3.2 Pack Current Accuracy
      3. 3.3.3 Auxiliary Power and System Current Consumption
      4. 3.3.4 Cell Balancing
      5. 3.3.5 Protection
      6. 3.3.6 Working Modes Transition
  9. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 BOM
    2. 4.2 Tools and Software
    3. 4.3 Documentation Support
    4. 4.4 Support Resources
    5. 4.5 Trademarks
  10. 5About the Author

1 System Description

Li-ion and LiFePO4 batteries are increasingly used in battery packs to achieve higher capacity and energy with equal or lower volumes and equal or lower weight for the following equipment:

  • Telecom and servers battery backup unit (BBU)
  • Energy Storage Systems (ESS)
  • e-motorcycles
  • Portable power stations

Each of these devices benefit from the higher power and energy density and safe and environmentally-friendly Li-ion and LiFePO4 batteries. While this chemistry provides high energy density and thereby lower volume and weight as an advantage, these attributes are associated with safety concerns and a need more accurate and complicated monitoring and protections. These concerns include the following:

  • Undervoltage (CUV)
  • Cell overvoltage (COV)
  • Overtemperature (OT)
  • Both overcurrent in charge (OCC) and discharge (OCD)
  • Short-circuit discharge (SCD)

All of these concerns contribute to accelerating cell degradation and can lead to thermal runaway and explosion.

Therefore, monitor the pack current, cell temperature, and the voltage of each cell in case of unusual situations. The battery pack must be protected against all these situations. Good measurement accuracy is always required, especially the cell voltage, pack current, and cell temperature. Precision is necessary for accurate protections and battery pack state of charge (SoC) and stage of health (SoH) calculations. This is especially true for LiFePO4 battery pack applications because of the flat voltage. Another important feature for battery-powered applications is the current consumption, especially when in ship mode or standby mode. Lower current consumption saves more energy and gives longer storage time without discharging the battery too much.

This design focuses on very large capacity battery pack applications, such as BBU for telecommunications and servers, 48-V ESS, e-motorcycles, portable power station, and so forth. The design contains a BQ76952 battery monitor and protector to monitor each cell voltage, temperature, and pack current and protect the pack against all unusual situations. These situations include cell overvoltage, cell undervoltage, overtemperature, overcurrent in charge and discharge, and short-circuit discharge. Five pairs of N-channel MOSFETs are located in battery negative as switches to control the charge and discharge processes. With a 5-A sink and source current driver, this design has the capability to drive more MOSFETs to support larger battery capacity. This reference design supports isolated RS-485 communication to transfer battery pack data and receive commands and reserve isolated CAN transceiver to test the auxiliary power performance. This design does not support CAN communication since the MCU used in this design does not have an integrated CAN controller. This design carefully designs the auxiliary power architecture, which achieves very low ship mode (10 μA) and standby mode (100 μA) current consumption with a limited number of components and a simple control strategy.